Steampunk Crab Fort Art

When I looked at it, my first thought was of the walking fort from Jack Vance's 1964 novel The Killing Machine:

He wanted Patch to design and construct a walking fort in the semblance of a monster centipede, seventy-six feet long and twelve feet high... The fort... must be able to move at a speed of at least forty miles per hour on synchronized, smoothly operating legs...
(Read more about Vance's walking fort)

Now that I think about it, this might also be a drawing of an extremely aggressive traction city:

In happier times, London would never have bothered with such feeble prey. The great Traction City had once spent its days hunting far bigger towns than this, ranging north as far as the edge of the Ice Wastes and south to the shores of the Mediterranean...
(Read more about traction cities from Philip Reeve's Mortal Engines)